1. Field of the Invention
The present invention relates to input devices that allows coordinate input and switch input through an operation surface, and more particularly, to an input device equipped with an illumination mechanism that illuminates an operation surface.
2. Description of the Related Art
Conventionally, a coordinate input device called a touch pad is mounted in a mobile computer terminal device such as a notebook personal computer. The touch pad is a pointing device for operating a cursor or a pointer displayed on the screen of the terminal device, similarly to a mouse. When a user's finger or a pen tip (pointing member) touches an operation surface of the touch pad, the touch point is detected by a sensor, and the cursor or the pointer is operated in accordance with a coordinate value of the touch point or the displacement of the coordinate value by movement of the touch point.
Japanese Unexamined Patent Application Publication No. 2006-107307 discloses a coordinate input device in which an operation surface is illuminated by an LCD panel (light guide plate) with a front light provided on a sensor.
In this input device, however, a reflection plate is provided on the sensor, and a light guide plate having a prism surface is provided on the reflection plate. Although the sensor, the reflection plate, and the light guide plate are combined by being fixed at both ends by a fixing frame, particularly, the fixing strength between the reflection plate and the light guide plate is apt to be insufficient.
In order to solve this problem, it is conceivable to increase the mechanical strength by entirely joining an upper surface of the reflection plate and a bottom surface of the light guide plate with an adhesive such as a double-sided adhesive tape.
Unfortunately, the bottom surface of the light guide plate is formed by a prism surface having fine irregularities. If the prism surface is buried in the adhesive, it does not fulfill its function, that is, a light reflecting function. Further, since light leaks from the joint portion, the light guide efficiency decreases, and luminance on an illuminating surface (principal surface of the light guide plate) easily becomes nonuniform.
When the reflection plate and the light guide plate are simply fixed with the adhesive, an air layer is sealed between the prism surface and the reflection plate. For this reason, if the temperature changes, the air pressure in the air layer increases or decreases. When this stress is repeatedly caused, the joint portion is deteriorated.
Multiple electrodes are provided on a surface of a substrate that forms the sensor, and the surface of the sensor has irregularities formed by the electrodes and the substrate surface. For this reason, a space is easily formed between the upper surface of the sensor and the lower surface of the reflection plate, and the joint therebetween is apt to be insufficient.
While an LED covered with a case is disposed adjacent to an end face of the light guide plate so as to face the end face, the efficiency in guiding light emitted from the LED into the light guide plate is low.
Further, in this input device, marks are not optically displayed on the operation surface, and it is difficult to visually recognize an operation mode and an object to be operated.